Report Port toolkit risk profile LNG bunkering

Transcription

1 Report Port toolkit risk profile LNG bunkering Port of Rotterdam, Ministry of Infrastructure & Environment, Port of Antwerp, Port of Amsterdam and Zeeland Seaport Report No./DNV Reg No.: PP R2 Rev. 2, 28 August 2012

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3 Port toolkit risk profile LNG bunkering Table of Contents CONCLUSIVE SUMMARY INTRODUCTION LNG BUNKERING SYSTEM DEFINITION LNG Bunkering at a glance Bunker configurations Location Characterization of bunker parameters WHAT IS LNG? METHODOLGY AND SCENARIO DEFINITION Scenario s and parameters related to safety distances for passing ships Hazard identification and Loss of containment scenarios Selection of representative scenario Calculation of effect of representative scenario Risk distances to vulnerable objects What can go wrong: Loss of containment scenarios How bad? Consequence Modelling How often? Failure frequencies So What? Risk Assessment What do I do? Risk Management ASSESSMENTS RESULTS Safety distances for passing ships Discussion Risk distances to vulnerable objects Category 1 - LNG bunkering with a small bunker vessel Category 2 - LNG bunkering with a large bunker vessel Category 3 - LNG bunkering with a tank truck Category 4 - LNG bunkering from a bunker pontoon Category 5 - LNG STS transfer Discussion RISK MITIGATION AND FURTHER RESEARCH General risk mitigation measures Study specific Date : Page ii of iii

4 Port toolkit risk profile LNG bunkering 6 CONCLUSIONS REFERENCES Appendix 1 Appendix 2 Appendix 3 Appendix 4 Scenarios Nautical risk assessment of moored LNG bunker vessels Background parameters for risk calculation Results distances to 10-6 per year risk contour Date : Page iii of iii

5 CONCLUSIVE SUMMARY The Port of Rotterdam, the Port of Antwerp, the Port of Amsterdam and Zeeland Seaports are preparing for the arrival of LNG as a fuel. Large scale bunkering of LNG is novel and differs on several aspects from the bunkering of conventional marine fuels. LNG is stored at low temperatures and the development of a gas cloud in case of a potential release to the atmosphere requires insight into the risks which have to be translated into procedures for safe and practical operation during For successful incorporation of these activities into their current safety systems (e.g. guidelines, operational procedures) and operations they DNV has been asked to develop a harbour toolkit safety distances LNG bunkering to help identify (a) the safety distances for passing ships and (b) the risk distance to vulnerable objects such as residential housing, offices, hospitals etc. The toolkit will help get insight what safety/risk distance should be taken into account given a specified bunker configuration and as function of the number of bunkers. As such it can be used as a (first) screening tool for suitability of bunker locations in the port area. The Port of Rotterdam identified various LNG bunker activities in a port area. Those activities can be grouped in five different categories: 1) LNG bunkering from small inland bunker vessel to small vessels 2) LNG bunkering from large bunker vessel to seagoing vessels 3) LNG bunkering from trucks to small vessels 4) LNG bunkering from bunker pontoons to small vessels 5) LNG transfer from ship to ship The determination of the safety distances for passing ships is determined by a consequence based methodology, where a representative risk scenario and consequence are selected. The selection of the representative scenarios is based on a (desktop) hazard identification. DNV found that the calculated safety distance for categories 1, 3 and 4 are in line with the nautical safety distances that are prescribed in the existing Dutch shipping regulation BPR. The calculated safety distances for the categories 2 and 5 are significantly larger than the nautical safety distances that are currently prescribed in the existing Dutch shipping regulation BPR. The relatively large safety distances that are found for those categories could enforce additional rules for the LNG bunkering of large vessels in area with intensive nautical traffic. It may not give restriction on LNG bunkering activities in area where lower nautical activities take place and collision scenarios are less credible / likely. The risk distances to vulnerable objects are calculated using a Quantitative Risk Assessment (QRA) methodology which includes both frequency and consequences calculations of possible Loss of Containment (LOC) scenarios (e.g. hose leakage). DNV have calculated the risk distances to vulnerable objects towards the Dutch risk criteria for vulnerable objects, i.e /year. Date : Page 1

6 The risk distances that are found for the different categories vary from 10 to 510 meter, depending on the category, bunker parameters, ignition method and number of bunker activities. The risk distances for the categories 1, 2 and 5 are mainly caused by the scenario where ship collision results in a loss of containment of the LNG cargo (bunker) tank on the LNG bunkering vessel. It is found that lowering of the nautical activities in the bunkering area may reduce the risk distance. For areas where (very) low nautical activities take place the risk distance is driven by the rupture of the bunkering hose and leakage through a 25 mm hole. It is found that the risk distance of category 3 and 4 is independent of the nautical activities because the distance is driven by the scenario rupture of the bunkering hose and leakage through a 25 mm hole. Date : Page 2

7 1 INTRODUCTION Liquid Natural Gas (LNG) is becoming more and more interesting as fuel for shipping. One of the main reasons is the upcoming stringent requirements for emissions from ship engines following the adoption of Emission Control Area s as of A ship engine running on LNG is emitting significant lower amounts of NO x, SO x and particulate matter as well as reduces the output of CO 2 than a ships engines running on conventional fuels. Next to that costs saving may be achieved. In order to use LNG as a shipping fuel there is a need to develop a LNG bunkering infrastructure. Several bunkering configurations are possible to deliver the LNG to the vessel. An example of a LNG bunkering configuration already used today can be seen on the DNV LNG blog [1]. Figure 1: Screenshots bunkering film Large scale bunkering of LNG is novel and differs on several aspects from the bunkering of conventional marine fuels. LNG is stored at low temperatures and the development of a gas cloud in case of a potential release to the atmosphere requires insight into the risks which have to be translated into procedures for safe and practical operation during LNG bunkering activities. Different ports are preparing for the arrival of LNG as a fuel. For successful incorporation of these activities into their current safety systems (e.g. guidelines, operational procedures), the Port of Rotterdam, Ministry of Infrastructure & Environment, Port of Antwerp, the Port of Amsterdam and Zeeland Seaports asked Det Norske Veritas (DNV) to determine the following: Safety distances for the determination of exclusion zones related to passing vessels during LNG bunkering activities, i.e. what is a safe passing distance for other traffic related to an ongoing LNG bunkering activity? Risk distances to vulnerable objects, i.e. what should be the minimum distance between an LNG bunker location and (fixed) vulnerable objects such as residential housing, offices, hospitals etc. based on the quantified risk. The purpose is to develop a risk-based toolkit, Date : Page 3

8 with which suitable locations for LNG bunkering activities can be identified in the port at any given time. Concerning the bunkering of LNG a significant amount of uncertainties still exist, e.g. related to ship designs (both for bunker vessel and recipient vessel), vessel types, bunkering equipment, process parameters etc. as there is only a limited number of LNG bunker stations operational to date In this study considerable effort has been made to make defendable assumptions but in case choices needed to be made the conservative option have been chosen in an attempt not to underestimate the risks related to LNG bunkering. And although in this study a lot of effort has been put in making the assessment as detailed and realistic as possible, future real life bunker configurations might have different parameters and characteristics. As such the results presented should be interpreted with care and as a minimum real life situations should be verified in detail to see whether their parameters are in line with the assumptions made in this study before conclusions are drawn based on this study. The report outline is as follows: Chapter 2 gives an overview of the LNG bunkering system definition. This chapter include a brief overview of the history of LNG and a description of the categorised LNG bunkering activities considered in this study. Next, a brief overview of the (safety) characteristics of LNG is presented in Chapter 3. Chapter 4 describes the applied methodology and scenario definition to determine the safety and risk distances. A detailed assessment of the results is provided in Chapter 5. Chapter 6 provided general and specific mitigation measures to reduce the risk that is found in Chapter 5. The report ends with Chapter 7 in which the main findings are summarised and conclusions are drawn. Date : Page 4

9 2 LNG BUNKERING SYSTEM DEFINITION In order to correctly assess and quantify the risks of LNG bunkering definition of the following key aspects are important: The configuration of bunkering: several bunkering configurations are feasible and each configuration has specific risks; The location of bunkering: the vicinity and number of passing vessels, presence of ignition, distance to vulnerable objects and such all can have a significant influence on the risk level; Bunker parameters: the number of bunker operations, the volume of the LNG flow, and the characteristics of safety equipment, e.g. time needed to close Emergency Shut Down (ESD) valves and other also have a significant impact on the risk level. In the paragraphs below a more detailed description of these various aspects is given. A short description of the LNG bunker process is also presented. 2.1 LNG Bunkering at a glance The typical main steps in a bunkering process are: Approach of the bunker vessel Setting up mooring arrangement Grounding and connecting of the bunker hoses; Inerting and purging of the filling lines; The bunker transfer; Stripping, purging and inerting of filling lines; Disconnecting of grounding and bunker hoses. The figure below is an illustration of the different elements in a LNG bunkering transfer chain. Focus is on the different equipment and the systems involved. Date : Page 5

10 Figure 2: Different elements in a LNG bunkering transfer chain LNG fuelled ships have bunkered successfully for ten years, since the first LNG fuelled ship a car and passenger ferry named Glutra was put into operation in Currently, a total of 26 LNG fuelled ships are in operation, and ~30 more new-builds have been ordered. In addition, some conversions are planned for convention fuelled ships. The bunkering operations currently in use for LNG fuelled ships in Norway are bunkering from trucks or from a land based tank via a fixed installation on pier or jetty. Trucks are common due to small scale supply, long distances between LNG production sites and bunkering sites, as well as between locations where the LNG fuelled vessels operate. Last year a LNG bunkering JIP in the Netherlands (LESAS project) started to investigate the possibility of LNG ship bunkering. Recently, the same initiative is launched in Singapore. The LNG bunkering JIP in Singapore identified the (manual) bolted connection of LNG hoses, as used in Norway at the moment, to be disputable. They prefer breakaway couplings which can be equipped with ESD2 option for rapid disconnection of the transfer hose / from the ship. Next to that the loading and unloading of cryogenic substances has been around for decades. Date : Page 6

11 2.2 Bunker configurations The Port of Rotterdam has identified various LNG bunker configurations in a port area and created a virtual port to visualise those bunker configurations. This virtual port is known as the Beanport after its creator Cees Boon. An overview of the Beanport is found in Figure 3. Some of these bunker configurations are classed as land base, e.g. bunkering from an onshore storage facility. These configurations are not part of the scope of this study. Instead this study focuses on the water based configurations with one addition: the bunkering of small vessels by truck. The water based configurations can be divided in five different groups: 1) LNG bunkering from small inland bunker vessel to small vessels 2) LNG bunkering from large bunker vessel to seagoing vessels 3) LNG bunkering from trucks to small vessels 4) LNG bunkering from bunker pontoons to small vessels 5) LNG transfer from ship to ship Each group is discussed in more detail and represented in figure 3 below. Figure 3: Overview of the LNG bunkering configurations in Beanport Date : Page 7

12 1) Bunkering of LNG from a small inland bunker vessel Small inland bunker vessels will load LNG from large scale or intermediate LNG terminals and transport it to bunker locations. At the bunker location the LNG is bunkered to small (inland) vessels through a flexible hose. The size of the bunker barge is strongly depending on the number of bunker operations and the bunker volume of the recipient vessel to be bunkered. Bunkering of short sea vessels and short sea Ro/Ro ferries does require more LNG bunker volume than inland vessels. The bunkering of LNG from a small inland bunker vessel will take between 1 or 2 hours depending on the LNG demand of the bunkered vessel and the bunkering flow rate. Bunkering flow rates vary from 80 to 500 m 3 /h. The volume of LNG per cargo tank is limited for small inland bunker vessel. The ADN [1] limit the volume of cargo tanks for standard inland vessel to 380 m 3, which means that cargo tanks of bunker vessels cannot be constructed above this threshold value. Bunker barges which will transport more LNG must be equipped with multiple cargo tanks. After special permission the ADN [1] allows cargo tanks with a volume up to 1000 m 3. To comparison; The Pioneer Knutsen, which is at the moment the only LNG small bunker vessel in operation, contains two spherical stainless steel 550 m 3 cargo tanks. This bunker vessel operates at 3 bar(a) [4]. 2) Bunkering of LNG with use of a large LNG bunker vessel Large LNG bunker vessels will load LNG from large scale or intermediate LNG terminals and transport it to the bunker locations. At the bunker location the LNG is bunkered to small vessels which could vary from tankers to large container ships. The size and main dimensions of small scale LNG carriers can vary significantly, depending on different market demands, draught and other physical limitations of the ports and bunker sites to be used. Typical cargo capacity for small scale LNG carriers may be approximately to m 3, but smaller and bigger vessels exist. According to the information received by the Port of Rotterdam the large container ships require a maximum bunker volume of m 3, which means that the entire volume of a large LNG bunker vessel is needed to bunker one container vessel. The LNG bunkering time of vessels in this study is limited to 7 hours. To meet the required bunkering volume in 7 hours LNG is bunkered by 3 flexible hoses. Bunkering flow rates per hose vary from 500 to 1000 m 3 /h. 3) Bunkering of LNG with use of LNG tank truck Regional land-based distribution of LNG can be carried out by heavy duty trucks, for example to serve nearby industries, other ports in the region and transportation within the port. LNG trucks are also used for transporting LNG from small scale liquefactions plants to customers who are not connected to the gas network. Examples of countries where LNG is distributed by trucks are Norway, Sweden, Finland, Belgium, Germany, the Netherlands, Poland, Spain, Turkey, China and Russia. LNG terminals with regional distribution of LNG by trucks are equipped with facilities for loading and unloading of trucks. Flexible hoses are used for the transfer of LNG between the terminal and the truck. The size of the truck is in Europe limited Date : Page 8

13 by the Accord européen relatif au transport international de marchandises Dangereuses par Route ADR to 40 m 3 [3]. A normal bunkering operation from a semi-trailer takes up to two hours including signing of documents and safety procedures. The actual pumping / transfer time is approximately one hour. According to the information received by the Port of Rotterdam short sea Ro/Ro vessels require a maximum bunker volume of 200 m 3, which means that multiple trucks are required to bunker a single Ro/Ro vessel. Inland vessel require less bunkering volume. The first LNG fuelled inland vessel, Argonon, requires 40 m 3 of LNG. This inland vessel is bunkered with a single LNG truck. 4) Bunkering of LNG with use of a fixed land based tank/installation (bunker pontoon) Bunker pontoons and other small scale land based LNG installation will load LNG from LNG feeder vessels. Small scale land based LNG installation in port area could be as large as m 3. The volume of land based installations such as bunker pontoons, is much lower. Here, typical volumes up to 1000 m 3 can be expected. The smaller land based installations are likely to be used for the bunkering of inland vessels, harbour tugs or fishing vessels or even trucks. The bunkering of LNG from small scale installations to inland vessel will take approximately 1 hour depending on the LNG demand of the bunkered vessel and the bunkering flow rate. Bunkering flow rates vary from 30 to 80 m 3 /h. 5) LNG transhipment on the buoys or dolphins (ship to ship transfer) Most of the cargo operations normally take place between the large or small bunker vessels and intermediate LNG storage terminals. Nevertheless, it is possible to transfer LNG from a LNG feeder to a bunker vessel. During this ship-to-ship (STS) transfer the LNG bunker vessel will moor alongside the LNG feeder to transfer LNG. The advantage of the transfer method is the absence of an immediately land based terminal to transfer LNG to bunker vessels. The flow at which the LNG is transported is highly depending on the size of the receiving bunker vessel. LNG STS transfer can be applied to both large and small bunker vessels. Date : Page 9

14 2.3 Location Although the outcome of this study will be used to assess the suitability of proposed bunker locations, a definition of representative locations is needed in order to reach this outcome. Together with the port of Rotterdam it was decided two simulate three situations: 1. An area with intensive nautical activity: The intensive nautical traffic area is defined as a location where large ships with high velocity will pass the moored LNG bunker vessel. The potential impact energy of this scenario is high due to the combination of large ships with high velocities. In the Port of Rotterdam area, de Oude Maas could be seen as a representative case for an intensive nautical traffic area. The average traffic density on the Oude Maas is estimated at approx. 108,000 ships per year. The majority of the ships are less than 140 meter and have a speed around 8 knots. This combination of length (mass) and velocity results in a high potential impact energy on the waterway. 2. An area with low nautical activity: The low nautical traffic area is defined as a location where the traffic density is less than the intense nautical traffic area. At this location the average velocity of the ships is low and large vessels are supported by tugs which limits the probability of collision. The potential impact energy at this location is low. Representative locations for this scenario could be found in the Caland canal area. The average traffic density on the Caland canal is estimated at approx. 48,500 ships per year. The majority of the ships is less than 140 meter and have a speed around 8 knots. At this location the combination of length (mass) and velocity also results in high potential impact energy on the waterway. However the number of ships is significantly smaller than the Oude Maas, which significantly reduces the probability of collision. 3. An area with very low nautical activity: The very low nautical traffic area is defined as a location where ships are going to be berthed. At this location the average velocity of the ships is low (<5 knots) and large vessels are supported by tugs which limits the probability of collision. The potential impact energy at this location is low. Representative locations for this scenario could be found in a dock in the Amazonehaven area. The average traffic density on the Amazonehaven area is estimated at approx. 4,200 ships per year. At this location the average velocity of the ships is low and large vessels are supported by tugs. The potential impact energy at this location is low. All three areas will be used for the simulation of the risk associated with LNG bunker activities. For each of the locations the width of the waterway is estimate on 300 meter. The locations are displayed in Figure 4. Date : Page 10

15 Figure 4: Overview of the location of nautical traffic areas. 2.4 Characterization of bunker parameters A final key aspect that influences the overall risk levels is the characteristics of the bunkering process itself: e.g. the volume of the LNG flow or the number of bunker activities has a significant impact to the overall risk levels. To account for this some assumptions had to be made. These assumptions are described below. Number of bunker activities Since the number of bunkering activities will increase over time (as more gas fuelled ships will become available) three levels of bunker activity have been defined per bunker configuration: an upper bound, mean and lower bound level. The number of bunker activities per level is an indication for the visualisation of the risk. They do not represent the expected number of bunker activities in the Port of Rotterdam. The upper bound level of bunker activities for the categories 1, 3 and 4 are 10 per day. The mean and lower bound level for these categories equal 5 bunker activities per day and 1 bunker activity per week. For the category 2 the upper bound level of bunker activities is 1 per day. The mean and lower bound level for category 2 equal 1 bunker activities per 2 days and 1 bunker activity per month. Date : Page 11

16 For the last category, category 5, the upper bound level of bunker activities is 3 per week. The mean and lower bound level for category 5 equal 7 bunker activities per month and 1 bunker activity per month. Process characteristics Since the actual bunkering infrastructure is not yet available there is uncertainty in what the bunkering process parameters such as flow and pressure will be. To solve this situation two sets of process parameters have been used based on current comparable processes as well as known designs. Per bunkering configuration a minimal and maximal process parameter set has been defined. The variations in parameters include flow, diameter, bunker time, number of hoses and ignition method. Quantification of these parameters is given in appendix I and the addendum [13]. It must be note that the risk calculation with the maximum parameter set is based on the conservative ignition method where the flammable cloud is ignited at its largest volume. The minimum parameter set is based on the less conservative ignition method where the actual ignition like passing ships are taken into account. More information regarding ignition is found in Appendix III. Based on the above the following simulation scenarios are possible for each of the five bunker configurations. This leads to a total of 90 simulation scenarios. Figure 5: Overview of various simulation scenarios per bunker category Date : Page 12

17 3 WHAT IS LNG? LNG is Liquefied Natural Gas and as such is the same gas (mostly consisting of methane) that is used for cooking in many homes. In its liquid state, LNG is not flammable, nor explosive. When LNG is heated and becomes a gas, the gas is not explosive if it is unconfined. Natural gas is only flammable within a narrow range of concentrations in the air (5% to 15%). Less air does not contain enough oxygen to sustain a flame, while more air dilutes the gas too much for it to ignite. Ignition without ignition source (auto ignition) is not possible in normal conditions. The temperature at which auto ignition may occur is above 500 C (in an air-fuel mixture of about 10% methane in air, the auto ignition temperature is approximately 540 C, while the auto ignition temperature for diesel oil is in the range of 260 C to 371 C). In the event of a spill, LNG vapours will disperse with the prevailing wind. Cold LNG vapour will appear as a white cloud. Parts of that cloud contain flammable concentrations of gas. The flammable concentrations of gas could be ignited, which can results in a jet fire, flash fire or explosion (if confined). The probability of explosion could be limited by a good design of the facility or vessel which is fuelled by LNG. This means that facilities or vessels should have an open design where confinement is limited, so no significant overpressures can be built up after ignition. Localized jet or flash fires would burn with intense heat. To keep the public at a safe distance, thermal exclusion zones are established for installation that handle LNG. When LNG is released the liquid droplets rain out and may form a pool of LNG. The LNG pool cannot be ignited but the flammable concentration above can. Ignition of the flammable concentration above the pool will result in a pool fire. For pool fires also thermal exclusion zones are established to keep the public safe. When skin touches an extremely cold body or LNG, heat is transferred from the skin and organs to the cold body or LNG. This will cause damage to the skin and underlying tissues. The normal functioning of the body may be disturbed by the cooling of internal organs, which will lead to a critical condition called hypothermia. The cooling of the brain or heart is very dangerous. Proper procedures and the use of protective clothing and equipment to prevent any contact with the LNG are hence imperative. Large scale exposure to LNG will cause a fatality. However, the extremely low temperatures are not only hazardous to people. While stainless steel will remain ductile, carbon steel and low alloy steel will become brittle and fractures are likely if they are exposed to such low temperatures. Standard ship steel must therefore be protected and insulated from any possible exposure to LNG (e.g. using stainless steel drip tray etc.). Date : Page 13

18 4 METHODOLGY AND SCENARIO DEFINITION This chapter will discuss the methodology that is used for the determination of the safety distance to passing ships and the methodology that is used for the determination of risk distances to vulnerable objects. 4.1 Scenario s and parameters related to safety distances for passing ships The determination of the safety distances for passing ships is determined by a consequence base methodology, where a representative scenario and consequence are selected. The methodology is illustrated in Figure 6. Figure 6: Methodology of determination of safety distance Hazard identification and Loss of containment scenarios The selection of the representative scenarios is based on a (desktop) hazard identification which is focussed on hazards that can results in a loss of containment of LNG. During the hazard identification the cause, consequences and credibility of each of the hazards were identified. It is reasonable to assume to the overfilling of the fuel tank and improper boil of gas control do not occur if proper measures are in place. Hazards that arise from the intermediate LNG storage and/or fuel tank are not considered within the scope of this study. The other identified hazards that could occur are grouped in two different categories: Coupling failure Damage to the hose These two categories will be discussed below in more detail: Date : Page 14

19 Coupling failure Before the bunkering operation the hose is connected to the ship s manifold. The connection should be established by operators which could make an operational error while connection the hose. It is assumed that the system is tested (purged) prior to each bunkering operation, using nitrogen as inert gas. After the bunkering of LNG is finished the LNG hose is purged to prevent possible releases of LNG when disconnecting the hose. Nevertheless, a leak could occur at the flange face, resulting in an initial slow release, with little impact and growing to a wire cut across the flange face. The operator, which is present during the loading operation, would detect the leak and will shut down the installation. The shutdown action of the operator would isolate the leak and further release of LNG is prevented. A conservative estimate of the wire cut diameter/hole size that could occur during this incident would be between 5 10 mm. Hose Failure There are various failure mechanisms for (flexible) hoses. For the LNG bunkering purpose the following failure mechanisms where identified: Fatigue due to high pressure or low temperature; Ship securing/ mooring line failure; Collision of ships; Extreme weather conditions External impact due to lifting activities or maintenance The flexible hoses that are used for the bunkering of LNG are in European countries subjected to the Pressure Equipment Directive (PED). The PED prescribes periodic inspection of flexible hose if a certain threshold value of pressure and diameter is exceeded. European design standard EN [7] states that he maximum allowable working pressure in a hose should not be less than 10 bar(g). For pressures of 10 bar(g) and higher the PED prescribes a periodic inspection for hoses with a diameter above 2.5 inch. To ensure the technical integrity of the hose, the periodic inspection should be performed by an independent party. In industry it is also common to perform a visual inspection before the hose is connected. It is likely to assume that the inspection by bunkering company and independent party will secure the technical integrity of the bunker hose and failure or rupture of the hose is therefore not selected as credible scenario. During the bunker operation the receiving and bunker vessel are connected with mooring lines to prevent drifting. For all bunkering operations the receiving vessel is fixed to the shore as well. In case of collision the mooring lines will (partly) absorb the first impact energy. Colliding vessels with low amount of impact energy (e.g. low mass and/or velocity) will not have sufficient energy to rupture the mooring lines and loss of containment is not expected. For higher impact energies the mooring lines can fail and the tensile strength of the bunker hose could be the limiting factor for loss of containment. However coupling of flexible hose for gas transfer are equipped with a breakaway coupling to limit the spilled volume. Date : Page 15

20 The traffic density on the waterways around the Port of Rotterdam is high. Therefore collision scenarios are not negligible and collision of passing vessels could be seen as a credible hazardous scenario Selection of representative scenario In the above analyses two representative scenarios are identified as credible scenarios; leakage at the flange face with a hole diameter between 5 10 mm and disconnection of the breakaway coupling in case of a collision scenario. For bunker locations where the traffic density is relatively high the safety distance could be best determined with the disconnection of the breakaway coupling scenario. This selected scenario would be applicable for the Rotterdam port area where the traffic density is high Calculation of effect of representative scenario The results of the effects of representative scenarios are presented in the results chapter. Here the maximum effect of the representative scenario is used to determine the safety distance. 4.2 Risk distances to vulnerable objects The risk distances to vulnerable objects are calculated with using a Quantitative Risk Assessment (QRA) methodology. The QRA methodology is a well-known and widely accepted approach to determining risk levels associated with Loss of Containments (e.g. spills). The modeling practice is described in the Dutch Reference Manual Risk Assessments [4]. A QRA gives insight into the risks to human life of a certain activity by calculating the potential effects of a variety of scenarios as well as considering the probability of occurrence of these scenarios. A QRA tries to answer five simple questions. Beside each question, the technical term is listed for that activity in the risk assessment process: What can go wrong? Hazard Identification How bad? Consequence Modelling How often? Frequency Estimation So What? Risk Assessment What do I do? Risk Management Date : Page 16

21 4.2.1 What can go wrong: Loss of containment scenarios The individual risk contours will be calculated for all the 60 individual bunkering scenarios which are defined in Figure 5. A detailed scenario definition is provided in appendix I. Note that for each simulation scenario separate loss of containment scenarios are defined, which are reported in the next paragraph. During bunkering activities loss of containment (LOC) might occur due to various reasons (e.g. external ship collision, failure of hoses) and at several locations. As mentioned earlier, only potential LOC scenarios are taken into account during bunkering activities (i.e. failure of hoses or tanks on bunkering vessels due to external ship collision). LOC scenarios related to failures of storage tanks on bunkering vessels or inland bunker pontoons/tank trucks are outside the scope of this study and therefore not considered. The loss of containment scenarios used for the risk calculations per bunkering operation are specified in Table 1. Table 1: Loss of containment scenarios Scenario Description Hole size (mm) 1 Hose leakage 5 2 Hose leakage 25 3 Hose rupture Full bore 4 Tank leakage (only cat 1,2,5) Disconnection of hose due to Full bore ship collision The hose failure scenarios are representative for failure of hoses taken from the ARF document [6], which gives a suggestion for typical hole size diameters of leakages that could be taken into account when considering loss of containment during liquefied gas transfer in hoses or arms. The full bore rupture hole size varies for each bunkering activity/scenario setup depending on the typical hose diameter used (appendix I). For ship collisions between passing ships and bunkering or receiving vessels additional rupture scenarios are defined. The tank leakage scenario is only applicable in case ship collisions between passing ships and bunkering ship are possible. For a complete definition regarding potential loss of containment caused by ship collisions, a reference is made to Appendix II How bad? Consequence Modelling In parallel with the frequency analysis, consequence modeling evaluates the resulting effects if the accidents occur, and their impact on personnel, equipment and structures, the environment or business. In chapter 3 it is commented that natural gas is flammable in a narrow range of concentrations (5% to 15% in air). When ignited it can results in, jet,-, pool, - or flash fire depending on the time of ignition and place of ignition. Explosions could only occur when ignited flammable concentrations of gas are enclosed. The consequences of the fire are mostly dependent on the loss of containment parameters and the process conditions Date : Page 17

22 during the release. The loss of containment scenarios are discussed above. The process conditions are discussed below. Process conditions European design standard EN [7] states that he maximum allowable working pressure in a hose should not be less than 10 bar(g). According to internal within DNV a typical pressure in a bunker hose is around 5-6 bar(g). For this study a generic bunkering hose pressure of 5 bar(g) (stagnant, absolute pressure) is assumed, which is independent of type of bunkering activity. Pressure in the storage tank of the bunker vessel/pontoon or tank truck is estimated at 2 bar(g). The Swedish Marine Technology Forum (together with other organizations in a joint industry project) has developed a LNG bunkering Ship to Ship procedure, which is in principle accepted and approved by DNV [8]. The procedure states that a LNG bunker ship may be equipped with an insulated storage tank type C for liquefied natural gas, which could contain around 1000 m 3 at 3 bar(g) and -163 C. However, internal within DNV state that a typical operating pressure of LNG tanks in vessels would be closer to 2 bar(g). The latter pressure is used for the risk calculations for any type of bunkering vessel or LNG tank truck for that matter. A recent QRA study carried out by DNV confirms that storage pressure of LNG in tank trucks is typically equal to 2 bar(g). Based on the above mentioned pressures, it is reasonable to assume that the pump head is sufficient to realize the flows for each bunkering scenario provided by the Port of Rotterdam (ranging from 30 m 3 /hour for category 4, minimal transfer parameters and 1500 m 3 /hour for category 5, maximal transfer parameters). A typical LNG storage and transfer temperature of -162 C is used, under the assumption that bunkering vessels/installations have the ability to maintain the temperature constant by handling/escaping the boil-off vapors to, for instance, a compressor and subsequently a recondenser for liquefaction. Tank trucks are usually equipped with double-walled tanks with vacuum and insulation between the outer (carbon steel) and inner (aluminum) tank in order to maintain the low temperature How often? Failure frequencies The frequencies given in ARF are based on road or rail tanker transfer accident data and are therefore not suitable to use for this study. The technical notes of DNV for process failure frequencies [9], proposes a base frequency of 6.77 x 10-5 /visit for failure of loading arms (resulting in leakages). It is the best available data and is taken from the ACDS document from 1991 [10]. This frequency is based on liquefied gas transfers using articulated arms (rather than transfer hoses). Furthermore, incidents reported in the ACDS document are dominated by LPG spills rather than LNG spills. Nonetheless, the frequency is considered to be conservative best-estimate, if not upper bound for LNG transfers. The base frequency of articulated arms is factored with the following aspects to obtain the frequency that is used for transfer hoses: The base frequency is per visit and must be converted into failure frequency per hour per hose Date : Page 18

23 The base frequency is based on failure of articulated arms rather than hoses. Therefore a factor is applied to the base frequency. A reference is made to the Addendum [13] for the assumptions made to factor the base frequency. The frequency distribution between of respective loss of containment scenarios is based on the Dutch guideline for risk calculations (HARI) [4], which states that 10% of all leaks consist of rupture scenarios. The ARF document states that 10% of all small leaks are ruptures, which is more or less in the same order of magnitude. The frequencies of the smaller leaks (5, 25mm) are equally distributed, which is in agreement with the ARF document. Table 2: Loss of containment scenarios and likelihood Scenario Description Hole size Frequency Frequency (mm) (1/hour/hose) distribution (%) 1 Hose leakage x % 2 Hose leakage x % 3 Hose rupture Full bore 3.4 x % 4 Tank leakage (only cat 1,2,5)* Disconnection of hose due to ship Full bore - - collision* * Failure frequency is dependent on the level of nautical activity in the bunkering area (a reference is made to Appendix II for a specification of these frequencies) Intervention times of operators and EMS/ESD systems in place Measures such as the presence the operators, emergency shutdown systems (ESD/EMS) during transfer might mitigate discharge effects by tripping pumps or closing valves in case of a LOC. Small intervention times, which usually vary for each mitigation measure, are essential to significantly limit the amount of material being discharged during loss of containment. For operators, the intervention time is taken from HARI [4] and is equal to 120 seconds. The following conditions have to be met to ensure an intervention time of 120 seconds by an operator is achievable: The operator has the possibility to visual monitor the hose during the entire transfer. The presence of an operator is ensured by either a dead man s switch or a procedure in the safety management system. These measures should be inspected on a regular basis. Manual activation of an emergency shutdown during loss of containment by an operator should be well-documented in a procedure. The operator should be well-trained and is also familiarized with the procedures applicable. The emergency shutdown button should be positioned according to applicable rules and standards, which ensures fast, manual activation independent of release direction in case of loss of containment. The probability of failure on demand (PFD) of an operator is 0.1 and is also taken from HARI [4]. Date : Page 19

24 A fully automatic emergency shutdown system can detect leakages (gas detection, flow measurements) and are able to trip pumps/close valves automatically. Operation intervention is not necessary in case the EMS/ESD system is working properly. The PFD of automated shutdown systems is equal to (source: HARI). In the event that an automated shutdown system fails, an operator is still able to initiate the shutdown manually. Intervention time is assumed to be equal to 20 seconds for the 25mm hole and full bore rupture scenarios based on data provided by the Port of Rotterdam. It must be noted that the exact duration of intervention would be highly dependent on the design of the intervention system in place. It is reasonable to assume that a small leak will take longer to detect automatically and as such, the intervention time for the 5 mm hole size scenarios is set to 120 seconds. An EMS/ESD system and operator with each a response time of 20 and 120 s, respectively, is present at all bunkering vessels and installations (bunkering categories 1, 2, 4 and 5). Note that ESD systems might not be available for tank trucks (cat 3). For category 3, LNG bunkering with a LNG tank truck, only intervention of an operator is deemed possible. All flexible bunkering hose are equipped with a safety breakaway coupling. The breakaway coupling is a passive device that is located between the bunker hose and the receiving vessel. For external impact scenarios, like ship collision, the breakaway coupling will disconnect the bunker hose and immediately close the outflow area. The closure of the outflow area will be mechanical driven and last for less than a second. It is reasonable to assume that the closure of the breakaway coupling will be less than 5 seconds. Based on breakaway manufacturers information, the shut-off valves inside the breakaway coupling close immediately in the event of sudden disconnection (i.e. less than 1 second). As such, 5 seconds reaction time can be considered as a conservative estimate So What? Risk Assessment Up to this point, the process has been purely technical, and is known as risk analysis. The next stage is to introduce criteria which are yardsticks to indicate whether the risks are intolerable or negligible or to make some other value-judgment about their significance. This step begins to introduce non-technical issues of risk acceptability and decision making, and the process is then known as risk assessment. The Dutch risk criteria are implemented in the Decree External Safety Establishments For this study the Individual risk criteria is used to assess the calculated risk related to LNG bunkering activities. The Dutch Individual risk criteria states for vulnerable objects, a risk limit value of 10-6 per year must not be exceeded. For objects with limited vulnerability, the same value applies as an orientation norm and may be exceeded under certain conditions What do I do? Risk Management In order to make the risks acceptable, risk reduction measures may be necessary. The benefits from these measures can be evaluated by repeating the QRA with them in place, thus introducing an iterative loop into the process. Detailed investigation of risk mitigation measures and their impact of the risk calculation is not part of the scope of this study. However chapter 0 of this rapport gives a summation of risk mitigating measures that could be used to lower the risk related to LNG bunkering. Date : Page 20

25 5 ASSESSMENTS RESULTS This chapter will give an indication of the safety distance for passing ships as well as the risk distance to vulnerable objects. Both distances are given for the categories defined in chapter 2. The calculation of the distances is based on the scenarios defined in chapter 4. The background information, e.g. weather data, ignition and general risk parameters, that are used for the risk calculation are enclosed in Appendix III. 5.1 Safety distances for passing ships This section determines the indicative safety distance for all bunkering scenarios. Thereafter the determined safety distances are compared with the safety distances that are currently in place in the Rotterdam port area. The section is closed with a sensitivity analysis of two key parameters. As stated earlier the safety distance can best be determined based on the disconnection of the breakaway coupling scenario. The released volume and corresponding consequence is strongly depending on the flow rate and closure time of the breakaway coupling. For the determination of the safety distance the maximum bunker parameters are used. For the closure time of the breakaway coupling a value of 5 seconds is considered. The safety distance is based on the maximum effect of the selected scenario. The maximal effect for the disconnection of the breakaway coupling is a flash fire. A flash fire could occur when the released flammable cloud is ignited. This ignition could occur till the Lower Flammable Limit (LFL) concentration. The weather type wherefore the flash fire contour is calculated is stability class D and a wind speed of 5 m/s. The safety distance is determined as the LFL distance corresponding to the released volume of a disconnected breakaway coupling. The determined safety distances are summarised in Table 3. Table 3: Safety distances for the different bunker categories Bunker category 1 LNG bunkering with a small bunker vessel 61 2 LNG bunkering with a large bunker vessel 218* 3 LNG bunkering with a tank truck 49 4 LNG bunkering from a bunker pontoon 45 5 LNG STS transfer 235* Safety distance [m] (based on LFL) *the calculated safety distance for category 2 is based on the simultaneous disconnection of three hoses. For category 5 the safety distance is based on the simultaneous disconnection of two hoses. Date : Page 21

26 5.1.1 Discussion This section will compare the calculated safety distances for passing ships with the current nautical safety distances that are applicable in the Port of Rotterdam area. Hereafter the sensitivity of the closure time of breakaway coupling is discussed. The discussion section will be closed with a discussion about the applicability of the calculated safety distances for very low nautical risk areas. The term very low nautical risk areas must be seen in the context of the traffic density in the Port of Rotterdam. It may be possible that very low nautical risk areas in the Port of Rotterdam are seen as normal traffic densities in smaller ports. Current nautical safety distances Currently, the Rotterdam Port Management Bye-Laws (version: June 2011) [11] state that open ignition, like flames or areas where the temperature equal to or higher than the minimum ignition temperature of the substance in the cargo tank of the ship, are prohibited within a distance of 25 metres of the ship, with some exception cases. However, it is also suggested that this distance may have to be extended for ship of a specialized nature such as gas tankers. Furthermore, article 4.8 of the Port Bye-Laws states that activities related to the operation of the ship or objects on the ship have to be performed at least 25 metres away from dangerous substances or combustible material. Existing shipping regulations BPR [12] enforce a minimum passing distance of 50 metres between ships carrying specific explosive substances and other ships, unless ships are passing each other in opposite directions. A Swedish bunkering procedure [8] states that bunkering areas on both ships (bunkering vessel and receiving vessel) should be EX-classified and restricted area during bunkering. The size of the EX-zone shall be according to class rules for gas-dangerous space and 10 m horizontally on each side of the receiving ship bunker station plus the whole shipside vertically. The calculated safety distance for categories 1, 3 and 4 are in line with the nautical safety distances that are prescribed in the existing Dutch shipping regulation BPR and the Belgian shipping regulations. However, the safety distances are roughly a factor two higher than the distances in the Rotterdam Port Management Bye-Laws. The calculated safety distances for the categories 2 and 5 are significantly larger than the nautical safety distances that are prescribed in the existing Dutch inland shipping regulation and the distances in the Rotterdam Port Management Bye-Laws. The relatively large safety distances that are found for those categories restrict the LNG bunkering of large vessels in area with intensive nautical traffic. It may not give restriction on LNG bunkering activities in area where lower nautical activities take place and collision scenario are less credible. The sensitivity of the nautical activities is investigated in the following section. Sensitivity to Nautical activities For very low nautical risk area the collision of passing ships into the bunker operation may not be a credible scenario. In this case it would be better to selected the leakage at the flange Date : Page 22

27 face with a hole diameter between 5 10 mm. The driving force of this scenario is the pressure during the bunker operation. In section a pressure of 5 bar(g) is considered during the bunkering activity. For area where the nautical risk is not significant the determined safety distance for each category is 20 meter. From the assessment of the nautical activities is found that the safety distances could theoretically be reduced to 20 meter in case collision scenarios are not significant. However the safety distances cannot be less than the safety distances that is prescribed in the Dutch shipping regulations. Sensitivity of breakaway coupling closure time The closure of the outflow area of the breakaway coupling will be mechanically driven and will be accomplished in less than a second. However for the determination of the safety distances the closure time is conservative estimated on 5 seconds. The effect of the closure time of the breakaway coupling on the safety distance is investigated for the category 1 and 2. The results of this investigation are shown in Figure 7, where the left figure represents category 1 and the right figure category 2. The results of the sensitivity analysis show that the closure time of the breakaway coupling do not have a major effect within the investigated time range. The conservative time of 5 seconds to close to breakaway coupling does not have a significant influence on the safety distance, which means that the determined safety distance cannot be significantly reduced by quicker closure of the breakaway coupling. Figure 7: Safety distances for different closure time of the breakaway coupling; category 1 (left), category 2 (right) Date : Page 23

28 5.2 Risk distances to vulnerable objects The distances to the 10-6 /year individual risk (IR) contours for all bunkering scenarios defined in paragraph are visually displayed in the figures in this section. The distance to the 10-6 /year individual risk (IR) contours for the three levels of bunker activities per year (upper bound, mean and lower bound) are visualised with a dot. For practical reasons the dots are interconnected with a fitted line. The line between the calculated results does not give the exact distance to the 10-6 /year risk contour and should be used with care. More accurate results could be obtained in case more bunker activities per category are calculated. However this is not part of the scope of this project. It is important to mention that the results are based on the maximum and minimum parameter set as discussed earlier in section 2.4. The maximum parameter set is a summation of conservative assumptions (e.g. maximum flow, maximum diameter, maximum bunker time, maximum number of hoses and the most conservative ignition methodology). This means that the maximum parameter set gives an upper bound of expected risk level. The minimum parameter set is based on more average parameters and does not necessary represent the minimum / lower bound risk level. A detailed overview of all maximum and minimum parameters per bunker category is found in appendix I Category 1 - LNG bunkering with a small bunker vessel The distances to the 10-6 risk level for the different simulation scenarios from category 1 are given in Figure 8. From Figure 8 can be observed that for the maximum parameter set the distance to the 10-6 /year risk level differs for the intense and the less dense nautical traffic areas. The intense nautical traffic area does results in a higher distance to the 10-6 /year risk level. In the lower range of the nautical activities, there is no significant difference in distance. This means that the differences in distance to the 10-6 /year risk level for the low and very low nautical traffic area negligible. For the same figure could be seen that for minimum parameter set there is a difference in distance to the 10-6 /year risk level for each of the different nautical traffic area. In this parameter set a reduction of the nautical activities decreases the distances to the 10-6 /year risk level with %. The individual risk contours for maximum parameters are shown in Figure 9 where the orange line represents the 10-6 /year risk contour. The purple and light blue lines in Figure 9 represent the 10-5 /year and 10-4 /year risk contours. It is seen that there is only a small difference in distance between the 10-6 /year and 10-5 /year risk contour. The individual risk contours for minimal parameters are shown in Figure 10, where the same colours represent the different risk levels. Date : Page 24

29 Figure 8: LNG bunkering toolkit for category 1 Date : Page 25

30 Figure 9: IR contour for 5 bunker activities per day in cat 1, maximal parameters in intensive nautical risk traffic areas (left), low nautical traffic areas (middle) and very low nautical traffic areas (left). The orange line represents the 10-6 /year risk contour. Figure 10: IR contour for 5 bunker activities per day in cat 1, minimal parameters in intensive nautical risk traffic (left), low nautical traffic (middle) and very low nautical traffic (left). The orange line represents the 10-6/year risk contour. Date : Page 26

31 5.2.2 Category 2 - LNG bunkering with a large bunker vessel The distances to the 10-6 /year risk level for the different nautical scenarios from category 2 are shown in Figure 11. From the figure can be observed that for the maximum parameter set the 10-6 risk level do not significantly changes over the nautical scenarios. From this observation it can be concluded that the nautical activities does not have a significantly contribution the individual risk level of 10-6 /year. However for the minimum parameter set, changes in distance could be observed. In this parameter set a reduction of the nautical activities decreases the distances to the 10-6 /year risk level with 37%. In the intense nautical traffic scenario with minimum parameters the individual risk level of 10-6 /year is dominated by the collision scenario where a 250 mm hole is formed in hull of the large bunker vessel. The remaining risk is not related to collision scenarios and caused by full bore rupture of the bunkering hose. For low nautical traffic areas the collision scenarios are less contributing to the individual risk level of 10-6 /year, but still have a significant contribution. For the very low nautical traffic areas the collision scenarios are negligible. The individual risk contours for maximum parameters are shown in Figure 12 where the orange line represents the 10-6 /year risk contour. The purple and light blue lines in Figure 12 represent the 10-5 /year and 10-4 /year risk contours. It is seen that there is only a small difference in distance between the 10-6 /year and 10-5 /year risk contour. The individual risk contours for minimal parameters are shown in Figure 13, where the same colours represent the different risk levels. Date : Page 27

32 Figure 11: LNG bunkering toolkit for category 2 Date : Page 28

33 Figure 12: IR contour for 1 bunker activities per 2 days in category 2, maximal parameters in intensive nautical traffic areas (left), low nautical traffic areas (middle) and very low nautical traffic areas (left). The orange line represents the 10-6 /year risk contour. Figure 13: IR contour for 1 bunker activities per 2 days in cat 2, minimal parameters in intensive nautical traffic areas (left), low nautical traffic areas (middle) and very low nautical traffic areas (left). The orange line represents the 10-6/year risk contour. Date : Page 29

34 5.2.3 Category 3 - LNG bunkering with a tank truck The distances to the 10-6 risk level for the different simulation scenarios from category 3 are given in Figure 15 The difference in the distances to the 10-6 /year risk contour for intensive, low and very low nautical traffic areas that could be observed from Figure 15 is negligible. In this category there is no scenario where a possible LOC from the bunker vessel could occur. Bunkering operation is performed from a truck. The collision scenarios in this category could only results in rupture of the bunker hose. The LOC scenarios from the truck are not considered within the scope of this study. For most of the scenarios the 10-6 /year risk level is mainly caused by a combination of rupture and leakages through a 25 mm hole in the bunker hose. The risk caused by the rupture of the bunker hose during collision is negligible to the risk caused by rupture and leakage of the bunker hose during bunkering. With other words, the nautical activities in the surrounding of the bunker location do not have a significant influence on the 10-6 risk contour. Figure 14 shows the individual risk contours for maximum and minimum parameters at an intensive nautical traffic area. Figure 14: : IR contour for 1826 bunker activities in cat 3, intensive nautical traffic area, maximal parameters in (left), minimum parameters intensive nautical traffic area (right) Date : Page 30

35 Figure 15: LNG bunkering toolkit for category 3 Date : Page 31

36 5.2.4 Category 4 - LNG bunkering from a bunker pontoon The distances to the 10-6 risk level for the different simulation scenarios from category 4 are given in Figure 16. The risk drivers of category 4 do show a huge similarity to category 3. For most of the scenarios the 10-6 /year risk level is mainly caused by a combination of rupture and leakages through a 25 mm hole in the bunker hose. The LOC scenarios from equipment on the bunker pontoon are not considered within the scope of this study. It is expected that a separate risk assessment is performed for the permit application of the bunker pontoon and its equipment. Therefore collision scenarios that resulted in LOCs of the storage tank of the bunker pontoon are not considered. The risk caused by the rupture of the bunker hose during collision is negligible to the risk caused by rupture and leakage of the bunker hose during bunkering. This results in a limited difference between the distances to the 10-6 /year risk contour for the different nautical traffic areas. With other words, the nautical activities in the surrounding of the bunker location do not have a significant influence on the 10-6 risk contour. Date : Page 32

37 Figure 16: LNG bunkering toolkit for category 4 Date : Page 33

38 5.2.5 Category 5 - LNG STS transfer The distances to the 10-6 risk level for the different simulation scenarios from category 5 are given in Figure 17. The risk that is observed for the maximum parameter set seems to be independent of the nautical traffic area. For the minimum parameter set there is a significant difference between the three nautical areas. In general it can be concluded that the risk drivers of category 5 do show a huge similarity to risk driver in category 1 and 2. For most of the scenarios the 10-6 /year risk level is mainly caused by the collision scenario where a 250 mm hole is formed in hull of the large bunker vessel. Date : Page 34

39 Figure 17: LNG bunkering toolkit for category 5 Date : Page 35

40 5.2.6 Discussion From the previous sections it could be concluded that for the maximum parameter set the distance to the 10-6 risk level do not significantly changes over the nautical scenarios. The bunkering of LNG with small bunker vessel, category 1, is an exception where the intense nautical traffic area differs from the low and very low nautical traffic areas. Despite the small difference in distance between the low and very low nautical traffic areas, the 10-6 risk level of the low nautical risk area is dominated by the collision scenario where a 250 mm hole is formed in hull of the small bunker vessel. For the maximum parameter set of category 1 and 2 it is found that the difference in distance between the 10-6 and 10-5 risk level is small. A detailed analysis of the risk drives reveals that the 10-5 risk level is dominated by the hose rupture scenario where the ESD system works probably. This result clarifies why the distances of the low and very low nautical traffic areas do not significantly differ despite that they do not share the same risk driver. The maximum parameter set is based on the free field method which means that flammable clouds ignite when the lower flammable limit is reached. Table 4 shows the effect distances (Lower Flammable Limit (LFL)) of the different LOC scenarios from category 1. The largest effect distances are found for the collision scenario where a 250 mm hole is formed in hull of the small bunker vessel. Table 4: Effect distances LOC scenarios category 1 (likelihood is not taken into account) Scenario Effect distance [m] F 1.5m/s D 5m/s Full bore rupture ESD works Full bore rupture due to collision mm hole ESD works mm hole in bunker vessel The minimal parameter set is based on specific ignition that are present in the surrounding of the bunkering activity. In most of the cases the cloud is ignited before it reaches is LFL distance. Figure 18 shows the risk distribution for 5 bunker activities per day in category 1. The figure shows that for the minimal parameters the 10-6 /year risk level for intense and low nautical traffic areas is dominated by the collision scenario where a 250 mm hole is formed in hull of the small bunker vessel. In the very low nautical traffic area the 10-6 /year risk level is dominated by the scenario where the hose is ruptures and the ESD system works properly. The same trends can be seen for bunker activities in category 2. Date : Page 36

41 Figure 18: Risk distribution of 5 bunker activities per day in cat 1 for three different risk levels; left, intense nautical traffic; middle low nautical traffic, right; very low nautical traffic For the bunker categories 3 and 4 is observed that the distance to the 10-6 risk level do not significantly changes over the nautical scenarios. For the maximum parameter set of category 3 and 4 it is found that the distance to the 10-6 risk level is mainly caused by the hose rupture scenarios. An increase of the number of bunker activities shifts the risk driver to scenarios that are less likely to occur. For instance; for the lower bound activities the 10-6 /year risk level is mainly caused by the hose rupture scenario where the ESD system works probably, while for the higher bound activities the 10-6 /year risk level is mainly caused by the hose rupture scenario where the ESD system fails to work. The maximum parameter set is based on the free field method which means that flammable clouds ignite when the lower flammable limit is reached. Table 5 shows the effect distances (Lower Flammable Limit (LFL)) of the different LOC scenarios from category 3. The largest effect distances are found in case of rupture of the bunker hose. Table 5: Effect distances LOC scenarios category 3 (likelihood not taken into account) Scenario Effect distance [m] F 1.5m/s D 5m/s Full bore rupture ESD works Full bore rupture due to collision mm hole ESD works The minimal parameter set is based on specific ignition that are present in the surrounding of the bunkering activity. In most of the cases the cloud is ignited before it reaches is LFL distance. The left side of Figure 19 shows the risk distribution for 1 bunker activities per week in category 3. The right side shows the risk distribution for 10 bunker activities per day. The figure shows that for the minimal parameters and 1 bunker activity per week the 10-6 /year risk level is dominated by leakage through a 25 mm hole. For the lower risk levels, (10-8 /year) the dominant scenarios are shifted to the hose rupture scenarios. The figure also shows that for an increase in bunker activities (10 bunker activities per day) the dominant scenarios that Date : Page 37

42 contribute to the 10-6 /year risk level are shifted to the hose rupture scenarios. The same trends can be seen for bunker activities in category 4. Figure 19: Risk distribution in cat 3 for two different bounds; left, lower bound (1 bunkeractivity a week); right upper bound (10 bunkeractivities a day) Date : Page 38

43 RISK MITIGATION AND FURTHER RESEARCH This chapter gives an overview of risk mitigation measures that can improve the safety performance of the LNG bunker operations. Two set of measures are given: General mitigation measures that will ensure safe bunker operations, More study specific mitigation measures and topics for further research will be given to ensure safe LNG bunkering in the future. 5.3 General risk mitigation measures Risk levels could be reduced by two different sets of mitigation measures; mitigated measures that reduce the consequence of the loss of containment and mitigated measures that reduce the likelihood that loss of containment can occur. Mitigated measures should be focused on the prevention of loss of containment (LOC). Prevention of LOC scenario is often accomplished by technical and procedural measures. For bunkering of LNG the technical measures that could reduce the risk are: The technical integrity of the bunkering hose is secured by inspection. It is recommended that the bunker hose is visually inspected before each bunkering operation; Purging of bunker hose with for instance nitrogen before bunkering operations. Purging of transfer hose in common practice in industry for transferring large amounts of LPG. Leakages and coupling errors could be noticed when purging operations are performed; Specify rules sets for the distance between the hull of the bunker vessel and the LNG cargo tank for inland vessels. From the risk analysis of bunkering with inland vessels is concluded that the LOC of the cargo tank caused by collision is the main contributor the 10-6 risk level. Additional collision protection of hull on LNG bunker vessels More procedural measures that could reduce the risk are: Training of bunker operators. The safety aspects of bunkering of LNG can be compared with the bunkering of convention diesel. Bunkering personnel must be aware of the risks associated with LNG operations; Another procedural measure to prevent LOC scenarios is the bunker procedure which should be followed during the preparation and bunkering operation itself. At this moment most of the ports do not have a bunker procedure for bunkering of LNG. Before bunkering activities can be realised a bunkering procedure must be in place; Nevertheless, loss of containment could occur. If LOC occurs the consequences of the release must be kept as minimal as possible. Technical measures are often in place to minimise the release volume or/and consequence of the release: The release volume can be minimised by a proper ESD system that quickly detects the leak and shutdown the pumps and valves to prevent further outflow. The detection time of Date : Page 39

44 leakage is often depending on the amount of gas detectors and or/sensitivity of the excess flow valve. For LNG bunkering operations it could be recommended to install a ESD1 and ESD2 system where: - ESD 1 stop transfer pumps and compressors, hence providing a quick and safe means of stopping the transfer and isolating bunker vessel and recipient vessel systems - ESD 2 gives an additional level of protection by providing for a rapid disconnection of the transfer hose / loading arms from the ship. ESD 2 could, for example, be used if there is a fire on one of the ships (bunker vessel or recipient vessel). The domino effect to the bunker vessel and receiving ship can be minimised by equipping with a water spray or curtain. The water curtain sprays the affected area with water to prevent the deck steel from cracking. Another advantage is that the water curtain will dilute the released LNG cloud and lower the concentration of gas in the air. This measure reduces the distances at which the cloud is flammable. 5.4 Study specific The risk drivers for the different bunker categories are identified in chapter 5. Roughly two different risk drivers are identified: Category 1, 2 and 5; ship collision results in a loss of containment of the LNG cargo (bunker) tank. Category 3 and 4; rupture of the bunkering hose and leakage through a 25 mm hole For each of the risk drivers suggestions for mitigating measures or suggestions for further research will be given below: Nautical risk The individual risk level of 10-6 /year is for the category 1 and 2 activities mainly caused by the scenario where ship collision results in a loss of containment of the LNG cargo (bunker) tank. This conclusion is application for both intensive and low nautical traffic areas. The nautical risk calculations are based on a model that predicts the collision frequency. The predicted collision frequency is used as a starting point for the assessment of loss of containment frequency. The model predicts for the intensive nautical traffic area a collision frequency around 1.4 x 10-2 per year. For the low nautical traffic area the collision frequency is estimated at 3.8 x 10-3 per year. For a more detailed representation of the nautical risk these collision frequencies must be compared with the actual collision frequency in the Port of Rotterdam area. The calculated loss of containment frequency from LNG cargo tanks is strongly influenced by the layout of the bunker vessel. The key design parameters are the strength of the hull and the distance between the cargo tank and the hull of the bunker vessel. At this moment no inland Date : Page 40

45 bunker vessels do exist and estimation of the detailed technical layout of the vessel is difficult. For estimation of a more accurate loss of containment frequency, detailed investigation between the impact energy and the hole formation in cargo tanks of inland bunker vessels is necessary. The conclusion of this detailed investigation could lower the nautical risk significantly. Another option is to prescribe a minimum distance between the LNG cargo tank and the hull of the bunker vessel. For seagoing vessel this prescription is already in place: a minimum distance between the cargo tank and the hull is prescribed in the class rules of the classification societies. As most of the bunker vessels will be inland vessels class rules do not apply. A fourth option could be to lower the nautical risk by procedural measures. Although speed limitation of passing vessels and other procedural measures are not practical, they do lower the nautical risk significantly. Bunkering risk The individual risk level of 10-6 /year for the category 3 and 4 activities is mainly caused by rupture of the bunkering hose and leakage through a 25 mm hole. Risk reduction measures must be applied to the bunker activity itself since collision risk is negligible. The measures should be focused on limiting the amount of outflow or limiting the frequency at which the loss of containment can occur. The frequency at which rupture of the bunkering hose by external impact occur can for example be lowered by mitigation measures such as the application of a safety net above the bunker operation to mitigate the risk of falling objects (e.g. container couplings) or by limiting the number of maintenance and/or lifting activities in the surrounding of the bunker activity. The consequences of a release could be lowered by quick closure of valves and pumps in case of a loss of containment. Quick detection of the loss of containment is a key parameter in reduction of the possible consequences. For most of the categories in this study is assumed that an EMS/ESD system does have a response time of 20. For category 3, LNG bunkering with a LNG tank truck, it is assumed that only intervention measures of an operator are possible. In this case a response time of 120 seconds is taken into account. This response time could be significantly lowered if an automatic system is in place. Date : Page 41

46 6 CONCLUSIONS The Port of Rotterdam has identified various LNG bunker activities in a port area. Those activities can be grouped in five different categories: 1) LNG bunkering from bunker barges to small vessels 2) LNG bunkering from small scale LNG carriers to seagoing vessels 3) LNG bunkering from trucks to small vessels 4) LNG bunkering from bunker pontoons to small vessels 5) LNG transfer from ship to ship DNV has calculated the indicative safety distances for the determination of exclusion zones related to passing vessels during LNG bunkering activities. It is found that the calculated safety distance for categories 1, 3 and 4 are line with the nautical safety distances that are prescribed in the existing Dutch shipping regulation BPR. The calculated safety distances for the categories 2 and 5 are significantly larger than the nautical safety distances that are prescribed. The relatively large safety distances that are found for those categories could enforce additional rules to the LNG bunkering of large vessels in area with intensive nautical traffic. It may not give restriction on LNG bunkering activities in area where lower nautical activities take place and collision scenario are less credible. DNV calculates the risk distances to vulnerable objects for the Dutch risk criteria of 10-6 /year. The risk distances that are found for the different categories vary from 10 to 510 meter, depending on the category, bunker parameters, ignition method and number of bunker activities. The risk distance for the categories 1, 2 and 5 is mainly caused by the scenario where ship collision results in a loss of containment of the LNG cargo (bunker) tank. It is found that lowering of the nautical activities in the bunkering area may reduce the risk distance. For areas were (very) low nautical activities take place the risk distance is driven by the rupture of the bunkering hose and leakage through a 25 mm hole. It is found that the risk distance of category 3 and 4 is independent of the nautical activities because the distance is driven by the rupture of the bunkering hose and leakage through a 25 mm hole. Date : Page 42

47 7 REFERENCES [1] DNV LNG Blog; [2] European Argeement concerning the International Carriage of Dangerous Goods by Inland Waterways (ADN), United Nations Economic Commission for Europe (UNECE) and the Central Commission for the Navigation of the Rhine (CCNR), Geneva,2008 [3] Accord européen relatif au transport international de marchandises Dangereuses par Route (ADR), United Nations Economic Commission for Europe (UNECE), Geneva, 1968 [4] Pioneer Knutsen, website Vuyk Engineering Rotterdam B.V. [5] Reference Manual Bevi Risk Assessments version 3.2, National Institute of Public Health and the Environment (RIVM), Bilthoven, [6] ARF document T14 rev 1; Process equipment failure frequencies for transfer equipment, Det Norske Veritas, Høvik, [7] EN1472-2: Installation and equipment for liquefied natural gas Design and testing of marine transfer systems Part 2: Design and testing of transfer hoses, European Committee for standardization (CEN), Brussels, 2008 [8] LNG ship to ship bunkering procedure, Swedish Marine Technology forum Linde Cryo AB FKAB Marine Design Det Norske Veritas AS LNG GOT White Smoke AB, Sweden, [9] DNV process failure frequencies, standardized offshore leak frequencies, technical note 14, D.23 loading arms, rev0, Det Norske Veritas, Høvik, 2011 [10] ACDS; Major Hazard Aspects of the Transport of Dangerous Substances, Advisory Committee on Dangerous Substances, Health & Safety Commission, HMSO Major hazard aspects of the transport of dangerous substances, [11] Rotterdam Port Management Bye-Laws (version juni 2011), Part A Bulk Liquids General Physical checks-ups, section 37: naked light regulations are observed, Port of Rotterdam, Rotterdam, 2011 [12] Inland shipping police regulations ( Binnenvaartpolitieregelement ), article 6.18, subsection 2, Ministry of infrastructure and environment, the Hague, [13] Addendum; Input assumptions for risk calculations bunkering study Port of Rotterdam, Det Norske Veritas, Rotterdam, Date : Page 43

48 APPENDIX I SCENARIOS Date : Page 44

49 A high-level overview of all calculated scenarios is given in Figure 5, section 2.4. This appendix provides more detailed specifications on the applied LNG transfer parameters used for each scenario. Some transfer parameters vary per bunkering category and are divided into two extremes: minimal and maximal. Only the transfer parameters that vary per scenario are given in Table 6 (e.g. hose diameter, pump rate, number of hoses used per transfer, bunkering duration per transfer). For a complete overview of all used transfer parameters a reference is made to the addendum [13]. Table 6: Detailed bunkering scenario definition transfer parameters Scena rio Nautical activities Transfer parameters Ignition method Hose diameter (inch) Single pump rate (m 3 /hou r) Number of hoses used Duration per transfer (hours) Category 1 LNG bunkering with a small inland LNG bunker vessel 1.1 Intensive Maximal Free field Intensive Maximal Free field Intensive Maximal Free field Intensive Minimal Ignition Intensive Minimal Ignition Intensive Minimal Ignition Low Maximal Free field Low Maximal Free field Low Maximal Free field Low Minimal Ignition Low Minimal Ignition Low Minimal Ignition Very Low Maximal Free field Very Low Maximal Free field Very Low Maximal Free field Very Low Minimal Ignition Very Low Minimal Ignition Very Low Minimal Ignition Category 2 LNG bunkering with a large LNG bunker vessel 2.1 Intensive Maximal Free field Intensive Maximal Free field Date : Page 45

50 Scena rio Nautical activities Transfer parameters Ignition method Hose diameter (inch) Single pump rate (m 3 /hou r) Number of hoses used Duration per transfer (hours) 2.3 Intensive Maximal Free field Intensive Minimal Ignition Intensive Minimal Ignition Intensive Minimal Ignition Low Maximal Free field Low Maximal Free field Low Maximal Free field Low Minimal Ignition Low Minimal Ignition Low Minimal Ignition Very Low Maximal Free field Very Low Maximal Free field Very Low Maximal Free field Very Low Minimal Ignition Very Low Minimal Ignition Very Low Minimal Ignition Category 3 LNG bunkering with a LNG tank truck 3.1 Intensive Maximal Free field Intensive Maximal Free field Intensive Maximal Free field Ignition Intensive Minimal 3.5 Ignition Intensive Minimal 3.6 Ignition Intensive Minimal 3.7 Low Maximal Free field Low Maximal Free field Low Maximal Free field Low Minimal Ignition Date : Page 46

51 Scena rio Nautical activities Transfer parameters Ignition method Hose diameter (inch) Single pump rate (m 3 /hou r) Number of hoses used Duration per transfer (hours) 3.11 Ignition Low Minimal 3.12 Ignition Low Minimal 3.13 Very Low Maximal Free field Very Low Maximal Free field Very Low Maximal Free field Very Low Ignition Minimal 3.17 Very Low Ignition Minimal 3.18 Very Low Ignition Minimal Category 4 LNG bunkering from a bunkerpontoon 4.1 Intensive Maximal Free field Intensive Maximal Free field Intensive Maximal Free field Intensive Minimal Ignition Intensive Minimal Ignition Intensive Minimal Ignition Low Maximal Free field Low Maximal Free field Low Maximal Free field Low Minimal Ignition Low Minimal Ignition Low Minimal Ignition Very Low Maximal Free field Very Low Maximal Free field Very Low Maximal Free field Very Low Ignition Minimal 4.17 Very Low Ignition Minimal 4.18 Very Low Minimal Ignition Date : Page 47

52 Scena rio Nautical activities Transfer parameters Ignition method Hose diameter (inch) Single pump rate (m 3 /hou r) Number of hoses used Duration per transfer (hours) Category 5 Ship to ship LNG transfer 5.1 Intensive Maximal Free field Intensive Maximal Free field Intensive Maximal Free field Intensive Minimal Ignition Intensive Minimal Ignition Intensive Minimal Ignition Low Maximal Free field Low Maximal Free field Low Maximal Free field Low Minimal Ignition Low Minimal Ignition Low Minimal Ignition Very Low Maximal Free field Very Low Maximal Free field Very Low Maximal Free field Very Low Very Low Very Low Minimal Minimal Minimal Ignition Ignition Ignition Date : Page 48

53 APPENDIX II NAUTICAL RISK ASSESMENT OF MOORED LNG BUNKERVESSEL Date : Page 49

54 NAUTICAL RISK ASSESMENT OF THE MOORED LNG BUNKERVESSEL When the small inland or large LNG bunker vessel is moored and bunkering activities are ongoing, various accidental scenarios can be identified. For the scenario that a passing vessel collides with the docked LNG bunker vessel a detailed and quantitative assessment is performed using a DNV Energy Model. Bunkering activities do always take place in port areas where ship velocities are still relatively small. To enable a LNG bunker infrastructure LNG bunkering along waterways could be a possibility as well. Along the (inland) waterways velocities could be high. To assess the nautical risk an intensive, low and very low nautical traffic area is considered. All three scenarios are based on estimations of maritime traffic on three representative scenarios. This appendix will determine the loss of containment frequency of three identified nautical traffic areas (intensive, low and very low nautical traffic). Figure 20 shows the three different nautical traffic areas. Figure 20: Nautical traffic areas Date : Page 50

55 Methodology The risk analysis of the moored LNG bunker vessel is performed using DNV`s methodology for probabilistic hole assessment in moored LNG Carrier cargo tanks due to ship collisions. The methodology has been based on a DNV research program where the damage extents have been estimated for different ship sizes as a function of striking angles and bow types. This DNV energy model approach is developed to analyse only the risk of a moored LNG Carrier, since this activity is expected to be most relevant with regards to potential external risk exposure on land. The methodology is divided into a frequency and a collision part. In the frequency assessment average maximum impact energy is estimated with corresponding frequency. In the collision assessment experience data from previous studies is used to transform the average maximum impact energy to probability distribution for size impact damages. This applied probabilistic approach for collision risk assessment is visualized in the figure below. Figure 21: Probabilistic approach for collision risk assessment Date : Page 51

56 Frequency Assessment Estimation of maximum impact energy In the frequency assessment the vessel traffic passing a bunkering LNG vessel is dived into six classes of vessels, given by the properties of the passing vessels. These six classes are: Bulb bow vessels with length below 120 meters Raked bow vessels with length below 120 meters Bulb bow vessels with length between 120 and 180 meters Raked bow vessels with length between 120 and 180 meters Bulb bow vessels with length above 180 meters Raked bow vessels with length above 180 meters For each of the classes the vessels are grouped according to their type and displacement. The impact energy is estimated for each group and then summarised to weighted average impact energy for the vessel class, which is used as input in the collision assessment. Probability of collision The methodology assumes there are two dominant failure modes leading to collision: Steering gear failure Black out The probabilities for steering gear failure have been found from DNV`s internal database RiskNet. From this reference the following basis figures are applied: Steering gear failure : 8.3 x10-7 per nautical mile Black-out : 4.8 x10-6 per nautical mile The probability for one of these failure modes leading to an actual impact with an LNG Carrier dock at a berth is assumed to be a function of the geometric probability of hitting the docked carrier and the time available to implement mitigating actions. Geometric probability of hitting a passing carrier The geometric probabilities are a function of the length of the potentially stroked LNG Carrier, the distance to passing shipping lanes and physical obstacles such as breakwaters or shallows. Time to implement mitigating actions It is assumed that the probability of having time to implement mitigating action has a Weibull distribution. This means that the probability for implementing actions is very low up to a given time, where the probability increases sharply, to a time where very high probability that preventive action is implemented successfully. The typical actions that are Date : Page 52

57 implemented to mitigate striking incidents are assessed to be emergency anchoring, running engine full astern and re-powering of the vessel. In the methodology it is assumed that the probability of implementing mitigating actions starts to rise sharply around an average one minute. This is represented by a Weibull distributing with mean value of 60 seconds and a standard deviation of 31 seconds. The time available to implement mitigating actions are a function of the vessels speed and the distance from the shipping lanes and the potentially stroked vessel. Output from the frequency assessment is a probability for striking impact in to the LNG bunker vessel per vessel category with corresponding average maximum impact energy. Collision Assessment The relationship between the striking angles, the ship speeds and the absorbed deformation energy of the colliding ships is determined by, In the above formula the effect of striking location against the LNG vessel, x 2, is taken into account. A mean value of x 2 = 0.225*L LNG is assumed. For each of the selected striking ship sizes of L = 90 m, L = 140 m and L = 230 m the absorbed deformation energy has been calculated for a series of impact cases where the apparent striking angles and the ship speeds have been varied. The speed distribution of impacting vessels is adjusted relatively to the impact speed, based on the speed distribution found from the HARDER study, for impact at the time of collision. Date : Page 53

58 Hence, the energy is distributed, with the average max impact energy from the frequency assessment as the maximum impact energy and the downwards. Further, effect of the impact angle is included, where impact angels of 0 to 22,5 degrees and 167 to 180 degrees are assumed only to give glancing impacts, with no potential for cargo containment penetration. The remaining impact angels are grouped and represented in the structural model with impact angels of 45 degrees and 90 degrees. Results An estimation of vessel movements in the intensive, low and very low nautical traffic area was provided by the Port of Rotterdam. The DNV energy model however also needs additional input which is summed in the nautical part of appendix I. The collision frequency per category is calculated in the frequency assessment. For the intensive nautical traffic area it is found that the total collision frequency is around 1.4 x 10-2 per year. The total collision frequency for the low and very low nautical risk area is around 3.8 x 10-3 per year and 6.8 x 10-5 per year. Details about the segmentation of collision frequencies per category are given in Table 7 till Table 9. Table 7: Collision frequency of different types of vessels at intensive nautical traffic location Vessel type Collision frequency [/year] Bulb bow vessels with length below 120 meters 8.0 x Raked bow vessels with length below 120 meters 5.3 x Bulb bow vessels with length between x meters Raked bow vessels with length between x meters Bulb bow vessels with length above 180 meters 1 1 Raked bow vessels with length above 180 meters 1 1 Table 8: Collision frequency of different types of vessels at low nautical traffic location Vessel type Collision frequency [/year] Bulb bow vessels with length below 120 meters 2.3 x Raked bow vessels with length below 120 meters 1.5 x Bulb bow vessels with length between x meters Raked bow vessels with length between x meters Bulb bow vessels with length above 180 meters 3.4 x Raked bow vessels with length above 180 meters 2.3 x Average maximum impact energy [MJ] Average maximum impact energy [MJ] 1 On this representative waterway no vessel longer than 180 meters are recorded Date : Page 54

59 Table 9: Collision frequency of different types of vessels at very low nautical traffic location Vessel type Collision frequency [/year] Bulb bow vessels with length below 120 meters 4.0 x Raked bow vessels with length below 120 meters 2.7 x Bulb bow vessels with length between x meters Raked bow vessels with length between x meters Bulb bow vessels with length above 180 meters 5.2 x Raked bow vessels with length above 180 meters 3.4 x Average maximum impact energy [MJ] It must be noted that the collision frequencies are highly theoretically and may not represent the actual collision frequency in the Port of Rotterdam area. The collision frequency also represents all theoretical collision and not only the collisions which will results in a loss of Containment of LNG. The probability of Loss of containment is made in the collision assessment. The frequency assessment is followed up by the collision assessment where the probabilities of certain indentation depths into a moored LNG Bunker vessel are calculated. Graphical representations of indentation depths for the three nautical traffic areas are given in Figure 22. More details regarding the indentation depths for the nautical traffic areas are found in Table 10 till Table 12. Date : Page 55

60 Figure 22: Probability of indentation for intensive, low and very low nautical traffic areas Date : Page 56